TY - JOUR T1 - Evidence of selection bias in preterm survival studies: a systematic review JF - Archives of Disease in Childhood - Fetal and Neonatal Edition JO - Arch Dis Child Fetal Neonatal Ed SP - F79 LP - F84 DO - 10.1136/fn.84.2.F79 VL - 84 IS - 2 AU - D J Evans AU - M I Levene Y1 - 2001/03/01 UR - http://fn.bmj.com/content/84/2/F79.abstract N2 - OBJECTIVE To determine by how much selection bias in preterm infant cohort studies results in an overestimate of survival.DESIGN Systematic review of studies reporting survival in infants less than 28 weeks of gestation published 1978–1998. Studies were graded according to cohort definition: A, stillbirths and live births; B, live births; C, neonatal unit admissions. Proportions of infants surviving to discharge were calculated for each week of gestation.RESULTS Sixty seven studies report data on 55 cohorts (16 grade A, 23 grade B, 16 grade C). Studies that are more selective report significantly higher survival between 23 and 26 weeks of gestation (grade C > grade B > grade A, p < 0.01), exaggerating survival by 100% and 56% at 23 and 24 weeks respectively.CONCLUSION To minimise the potential for overestimating survival around the limits of viability, future studies should endeavour to report the outcome of all pregnancies for each week of gestation (terminations, miscarriages, stillbirths, and all live births). ER -